The present invention relates to a method of and apparatus for testing a workpiece. More particularly this invention concerns a control system usable in combination with a spark-discharge apparatus and a spectrographic testing apparatus for determining the composition of an alloy.
It is known to test an alloy by positioning it on a contact electrode and spacing it by a gap from a counter electrode. A unipolar electrical pulse is then passed between the counter electrode and the workpiece to generate an arc or a spark of long duration. The light of this arc is diffracted into a spectrum having lines each corresponding to one of the components of the workpiece. Photocells arrayed to receive the respective lines form respective electrical signals having strengths corresponding to the intensities of the respective lines.
In our above-cited applications there is disclosed a system for integrating the several electrical signals corresponding to the lines for the various components of the workpiece and for thereafter comparing these integrated signals with reference values. The reference values may be derived from the signal corresponding to the basis metal or main component of an alloy so that when used in a steel plant, for example, the iron of the alloy is employed as a base value against which the others are compared. When any of the alloy components varies beyond a predetermined range from the desired composition an error signal is generated and the operator of the machine can appropriately alter the production process or eliminate the workpiece from the process.
A problem with such devices is that they are frequently extremely large and bulky and require carefully trained personnel to operate them. Thus a highly trained technician must stand ready at the apparatus in order to set it up to make the various test.
Another disadvantage of others of the known systems is that the counter electrode frequently oxidizes. Thus the first readings, at least, will often be falsified by the oxide layer on the counter electrode. Furthermore the workpieces themselves are almost invariably oxidized so that once again several readings must be taken before the results can be relied on.
Yet another disadvantage of the known testing machines is that calibrating them is a very complicated procedure which must usually be conducted by a trained metallurgist or the like. To do it the various controls of the machine must be set up in an altogether different manner as is the case when the machine is used simply for testing workpieces seriatim, and thereafter the machine must be programmed to make simple readings. Also inexact positioning of the counter electrode often gives an arc that generates inadequate light so that false readings occur during the inadequate time the device has to charge up. Another disadvantage is that the machine either cannot lock in once it makes a reading indicating that the workpiece is of an undesirable composition, or if it locks in a skilled technician again is required to restart the device.